The present invention relates to a semiconductor device capable of protecting its circuit arrangement from analysis, thereby making it difficult to imitate or duplicate the circuit or to alter information.
A semiconductor device is generally composed of a multiplicity of semiconductor elements provided on a substrate, and wirings provided between electrodes of the semiconductor elements. In such a semiconductor device, to protect the foregoing structure from effects of the external atmosphere, such as xcex1 rays, moisture, or stress, a circuit section is protected with a protective film with insularity made of silicon oxide, silicon nitride, or the like. This enables prevention of malfunctions caused by moisture intrusion, etc., changes of characteristics caused by stress, and the like.
Besides, some circuit sections of semiconductor devices are developed as a result of long-time studies, or some are very unique, which are preferably protected so as not to be imitated or copied by others. Moreover, some circuits of semiconductor devices are memory elements in which important information is stored, which are preferably protected so that information therein should not be altered.
The protective films described above are intended to merely protect the circuit section from the external atmosphere, and as to the optical aspect, many of them exhibit good permeability with respect to visible light and far infrared radiation, allowing the circuit section to be easily observed through the protective film by means of visible radiation microscopes or infrared radiation microscopes. This could permit the circuit section to be imitated or copied, and information in memory elements to be altered. Therefore, conventionally, structures as described below have conventionally been adapted to prevent this.
(1) In a structure disclosed in the Japanese Publication for Laid-Open Patent Application No. 165129/1989 (Tokukaihei 1-165129 [Date of Publication: Jun. 29, 1989]), as shown in FIG. 14, an integrated circuit includes a circuit section 40 in which a multiplicity of semiconductor elements provided on a semiconductor substrate are mutually connected via wirings, and a protective film 42 with insularity that covers the circuit section 40. The protective film 42 is made from, for instance, silicon nitride, in which a metallic film 43 with conductivity is provided. Parts of a surface of the circuit section 40 where security protection is not required is covered with only the protective film 42, while regions of main sections are covered with a lower layer 42a of the protective film 42, a metallic film 43, and an upper layer 42b of the protective film 42 in the stated order.
This ensures that in etching the protective film 42, an entirety of the protective film 42 is removed from regions where security protection is not required, while only the upper layer 42b of the protective film 42 on the metallic film 43 is removed in the regions of the main sections covered with the metallic film 43. Thus, since the metallic film 43 is not removed, the main sections that require security protection are not exposed, thereby being invisible. Besides, even if the metallic film 43 is removed by etching in the foregoing state, wiring patterns 41 that are made from the same material as that of the metallic film 43, for instance, aluminum, are also removed, resulting in that the circuit section 40 cannot be analyzed. Thus, by covering the main sections of the circuit section 40 with the metallic film 43 having conductivity while inserting the insulating protective film 42 therebetween, the integrated circuit is protected from being imitated or duplicated by others.
(2) The Japanese Publication for Laid-Open Patent Application No. 154674/1999 (Tokukaihei 11-154674 [Date of Publication: Jun. 8, 1999]) discloses a structure as shown in FIG. 15. More concretely, on one main surface of a semiconductor substrate 50 wherein an integrated circuit is formed, an insulator isolating layer 51 comprising silicon dioxide (SiO2) is deposited. In the insulator isolating layer 51, first and second wirings 52 and 53 that are made of aluminum (Al) and connected to the integrated circuit, and a shielding layer 54 made of Al are embedded and formed. Opening parts 54a and 54b are formed in the shielding layer 54, and connecting layers 55 and 56 made of Al are formed in the same layer as the shielding layers 54 in the opening parts 54a and 54b. Both ends of the connecting layer 55 are connected to cut-end parts 52a of the first wiring 52 through vias 57 made of tungsten (W). Both ends of the connecting layer 56 are connected to cut-end parts 53a of the second wiring 53 through vias 58 made of W. A surface-protecting layer 51b is formed on the surface of the shielding layer 54.
In this arrangement wherein the integrated circuit is shielded by the shielding layer 54 and the shielding layer 54 and the connecting layers 55 and 56 are made of the same material and formed in the same layer, an attempt to remove the shielding layer 54 by etching results in removal of the connecting layers 55 and 56 at the same time. Thus, by providing the shielding layer 54 that optically shields the foregoing wirings and by forming the connecting layers 55 and 56 as part of the foregoing wirings in the same layer in that the shielding layer 54 exists, it is possible to prevent the circuit in an operating state from being observed, hence to protect the operating state of the circuit from analysis for the purpose of illegal act.
(3) The Japanese Publication for Laid-Open Patent Application No. 270562/1998 (Tokukaihei 10-270562 [Date of Publication: Oct. 9, 1998]) discloses a structure as shown in FIG. 16. This structure has a multi-wiring structure in which a polysilicon gate and a wiring 62 are formed on a silicon substrate 61 and a metallic first layer wiring 64 and a metallic second layer wiring 66 are formed on insulating films 63 and 65, respectively. Incidentally, the metallic second layer wiring 66 is covered with a passivation film 67. Above the insulating film 65, an opaque conductive shielding film 60 is formed in the same layer where the metallic second layer wiring 66 is provided, with a gap kept therebetween.
In this structure, the integrated circuit is shielded by the conductive shielding film 60, and further, removal of the conductive shielding film 60 results in breaking the wirings in the same layer. By providing a system to prevent the inner part of integrated circuit from optically being observed, the reverse engineering of a semiconductor integrated circuit is prevented.
The above-described structures, however, have the following problems.
In the structure of (1), since the upper layer 42b made of the same material as that of the lower layer 42a is present on the metallic film 43, stopping the etching of the protective film 42 when the metallic film 43 is exposed makes it possible to etch exclusively the metallic film 43. This allows to make the lower circuit structure observable, thereby making analysis of the circuit possible.
The structure of (2) is intended to damage the wirings upon removable of the shielding metallic film so as to prevent analysis of the circuit operations. After chemically or physically removing a protective film above the shielding layer 54 and the connecting layers 55 and 56 in the same layer, photolithography may be applied to expose only the shielding layer 54, whereby removal of only the shielding layer 54 as shielding metallic film is enabled. In the structure of (3) as well, the conductive shielding layer 60 can be removed in an identical manner.
Thus conventionally available are the methods that easily overcome the schemes for preventing a circuit from being copied, duplicated and for preventing recorded information from being altered, and hence complete protection of circuit information is difficult.
An object of the present invention is to provide a semiconductor device that effectively prevents observation of the circuit, and surely protects the internal circuit from analysis.
To achieve the foregoing object, a semiconductor device of the present invention includes (i) a circuit section formed on a semiconductor substrate, (ii) a main body wiring that is provided on the semiconductor substrate and that is connected with the circuit section, (iii) a light blocking film provided so as to cover a principal part of the circuit section, and (iv) a coating film that is laminated so as to completely cover the light blocking film and that is made from a film material having corrosion resistance.
With the foregoing arrangement wherein the light blocking film that has a light blocking property thereby exhibiting poor permeability with respect to visible light and far infrared radiation is provided so as to cover the principal part of the circuit section, recognition of the lower circuit pattern can be made impossible. Further, since the coating film is made from a material having corrosion resistance, it is difficult to remove the coating film with use of a liquid chemical or the like.
Alternatively, a semiconductor device of the present invention may include (i) a circuit section formed on a semiconductor substrate, (ii) a main body wiring that is provided on the semiconductor substrate and that is connected with the circuit section, and (iii) a light blocking film that is laminated so as to cover a principal part of the circuit section and that exhibits corrosion resistance.
The foregoing arrangement in which the light blocking film has corrosion resistance makes the light blocking film unremovable. Moreover, since the light blocking film is provided so as to cover the circuit section, it is possible to make the lower circuit pattern invisible. Besides, another corrosion-resistive film for protecting a light blocking becomes unnecessary.
For a fuller understanding of the nature and advantages of the invention, reference should be made to the ensuing detailed description taken in conjunction with the accompanying drawings.